The BMR formula uses the variables of height, weight, age and gender to calculate the Basal Metabolic Rate (BMR). This is more accurate than calculating calorie needs based on body weight alone. The only factor it omits is lean body mass and thus the ratio of muscle-to-fat a body has. Remember, leaner bodies need more calories than less leaner ones. Therefore, this equation will be very accurate in all but the very muscular (will underestimate calorie needs) and the very fat (will over-estimate calorie needs).

Once you know your BMR, you can calculate your Daily Calorie Needs based on your activity level using the Harris Benedict Equation.

Harris Benedict Formula

The Harris Benedict Equation is a formula that uses your BMR and then applies an activity factor to determine your total daily energy expenditure (calories). The only factor omitted by the Harris Benedict Equation is lean body mass. Remember, leaner bodies need more calories than less leaner ones. Therefore, this equation will be very accurate in all but the very muscular (will under-estimate calorie needs) and the very fat (will over-estimate calorie needs).

If you are sedentary, multiply your BMR (1745) by 1.2 = 2094. This is the total number of calories you need in order to maintain your current weight.

Once you know the number of calories needed to maintain your weight, you can easily calculate the number of calories you need to eat in order to gain or lose weight:

- Calorie Needs to gain weight

Once you know the number of calories you need to maintain your weight (using our BMR Calculator in conjunction with our Harris Benedict Equation, you can easily calculate the number of calories you need in order to gain weight.

If you want to gain body weight, you need to consume more calories than you burn. One pound of body weight is roughly equivalent to 3500 calories, so eating an extra 500 calories per day will cause you to gain one pound a week.

For optimum health, if you increase your calories to gain weight then (health permitting) gradually increase your level of physical exercise in order to maintain or increase your lean body mass. The benefits of exercise on physical and mental health are well documented and shouldn't be ignored.

- Calorie Needs to lose weight

There are approximately 3500 calories in a pound of stored body fat. So, if you create a 3500-calorie deficit through diet, exercise or a combination of both, you will lose one pound of body weight. (On average 75% of this is fat, 25% lean tissue) If you create a 7000 calorie deficit you will lose two pounds and so on. The calorie deficit can be achieved either by calorie-restriction alone, or by a combination of fewer calories in (diet) and more calories out (exercise). This combination of diet and exercise is best for lasting weight loss. Indeed, sustained weight loss is difficult or impossible without increased regular exercise.

If you want to lose fat, a useful guideline for lowering your calorie intake is to reduce your calories by at least 500, but not more than 1000 below your maintenance level. For people with only a small amount of weight to lose, 1000 calories will be too much of a deficit. As a guide to minimum calorie intake, the AmericanCollege of Sports Medicine (ACSM) recommends that calorie levels never drop below 1200 calories per day for women or 1800 calories per day for men. Even these calorie levels are quite low.

An alternative way of calculating a safe minimum calorie-intake level is by reference to your body weight or current body weight. Reducing calories by 15-20% below your daily calorie maintenance needs is a useful start. You may increase this depending on your weight loss goals.

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Underweight Treatment

The best way to add weight is to increase your intake of complex carbohydrates, particularly whole grain ones. Foods like whole wheat bread, muffins, pasta, crackers, and bagels are good to include. Also, legumes and fruits would be wise choices.

In order to gain weight, you will have to eat more calories. You will need to include regular exercise and strength training into your lifestyle in order to prevent gaining too much weight as fat. And, as I mentioned, those extra calories should come mainly from additional carbohydrate.

To start, set up a realistic goal weight for yourself. You may need to resign yourself to a less than (what you may consider) an ideal weight. Make good nutrition your priority, and weight gain the second.

It is best to gain weight slowly and steadily. This will help to ensure that your weight gain is in the form of lean body mass and not excessive fat. Don't try to gain more than 1/2 pound a week.

Your body weight is controlled by the number of calories you eat and the number of calories you use each day. So, if you consume fewer calories than you burn, you will lose weight. You can do this by becoming more physically active or by eating less.

You didn't put on extra weight overnight so it is equally unrealistic to take it off quickly. Record a goal that you can reach in one month that is 4 to 8 pounds less than you weigh now. Set a goal you know you can achieve.

Here are some very simple changes that you can start today that will greatly improve your chances of weight loss success:

Eliminate Red Meat

If foods like burgers are basic to your current diet, cutting out red meat can go a long way in helping you make healthier meal choices. Build your meals around fish or poultry.

Cut out fried foods

Grill, bake, roast, broil or boil your food. This also means doing without French Fries and snack foods like Potato Strings, Chips,...

Start with a soup or a salad

By starting dinner with a soup or salad, you will curb your hunger, which will in turn help you keep portion sizes in check and prevent you from overeating.

Stop Cola consumption

For every 20 ounces of Coca-Cola you drink, you're consuming 250 calories. If you're trying to consume around 1500 calories a day in order to lose weight, you can blow your entire calorie budget on soda!

Drink water

Reach for the goalf of eight glasses a day. Even if you don't drink eight, you're drinking more than usual.

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Obesity Treatment

The method of treatment depends on your level of obesity, overall health condition, and motivation to lose weight.

Treatment includes a combination of diet, exercise, behavior modification, and sometimes weightloss drugs. In some cases of severe obesity, gastrointestinal surgery may be recommended.

If you are overweight, losing as little as 7-10 percent of your body weight may improve many of the problems linked to being overweight, such as high blood pressure and diabetes.

Slow and steady weight loss of no more than 1-2 pounds per week is the safest way to lose weight. Too rapid weight loss can cause you to lose muscle rather than fat. It also increases your chances of developing other problems, such as gallstones and nutrient deficiencies. Making long-term changes in your eating and physical activity habits is the only way to lose weight and keep it off!

Whether you are trying to lose weight or maintain your weight, you must improve your eating habits. Eat a variety of foods, especially pasta, rice, wholemeal bread, and other whole-grain foods. Reduce your fat-intake. You should also eat lots of fruits and vegetables.

Making physical activity a part of your daily life is an important way to help control your weight. Try to do at least 30 minutes of physical activity a day on most days of the week. The activity does not have to be done all at once. It can be done in stages: 10 minutes here, 20 minutes there, providing it adds up to 30 minutes a day.

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Body Fat Formula

If you are unable to use our Body Fat Calculator, or if you are interested in how your Body Fat Percentage is calculated, this page has the mathematical Body Fat Formula.

The best time to use this formula, is in the morning. Your body weight and waist measurements are the most accurate just after you wake up from 7-8 hours of sleep.

The formula below will not calculate your exact body fat percentage. The most accurate way is underwater weighing, but this formula should give you a consistent measurement you can use as a guideline so you can determine if you're losing body fat and/or muscle.

So, for this individual to achieve a lean, but healthy 18% fat, she would need to lose only 7 pounds of fat, reducing her weight from her current 130 pounds to 123 pounds. Losing more than 7 pounds means losing lean body mass (usually metabolically-active muscle tissue), which is clearly not desirable.

So before you decide that you need to "lose weight", remember to consider that "weight" consists of both lean body mass and body fat. Try to keep your weight loss goals realistic, and remember, keep the calorie-burning muscle, and lose only the fat.